Pressure fluid servomotor



Jan. 13, 1959 J. E, FORSLUND PRESSURE FLUID SERVOMOTOR 2 Sheets-Sheet 1 Filed March 30, 1954 Fig.1

INVENTOR.

Jc wAN ELIS FORSLUND I ATTO;

Jan. 13, 1959 J. E. FORSLUND PRESSURE FLUID SERVOMOTOR Filed March so, 1954 2 Sheets-Sheet 2 S FORSLUND JOHAN ELI RNEYS ATTO PRESSURE FLUID SERVOMOTOR Johan Elis Forslund, Skelleftea, Sweden Application March 30, 1954, Serial No. 419,893

2 Claims. (Cl. 121-46) The present invention relates to a hydraulic crane of the kind which comprises a piston adapted to be operated from a source of fluid under pressure and operatively connected to the lifting member of the crane, said piston being displaceable in a cylinder (the power cylinder) to a limit position corresponding to the most elevated position of the lifting member and rigidly connected with a cut-off member controlling the communication between the power cylinder and the source of fluid under pressure and movable in a separate cylinder normally in communication with the power cylinder and with the source of fluid under pressure, said separate cylinder being, along a major portion of its length, of larger diameter than said cut-off member but being diametrically reduced in the portion thereof situated towards the position of the cut-off member corresponding to said limit position.

The invention has for its object to enable, by purely hydraulical means, a smooth retardation of the move ment of the lifting member to be effected towards its limit position to thereby prevent the creation of harmful or damaging shocks.

The invention mainly resides in that said cut-01f member is in the form of a plunger or slide-valve sealingly slidable through said reduced portion of the separate cylinder and adapted by a slide-valve action, upon being displaced, progressively to cut off the communication be- ;tfiwegn the power cylinder and the source of pressure The source of pressure fluid suitably communicates with the slide-valve cylinder through one or more ports in the wall of the slide-valve cylinder and so disposed as to cause said port or ports to be covered by the slidevalve in the position thereof corresponding to the said limit position.

The invention will now be described more in detail, reference being had to the accompanying drawings in which:

Fig. 1 is a fragmentary longitudinal section of an ar rangement according to the present invention.

Fig. 2 is a fragmentary longitudinal section, to a smaller scale, of the same arrangement and related parts of the crane, the figure however illustrating the movable parts in different positions from those of Fig. 1.

Fig. 3 is a fragmentary longitudinal section through a portion of Fig. 2, but to a larger scale.

Referring now to the drawings more specifically, in the power cylinder 1 a piston 2 is longitudinally displaceable. The latter is formed in its top face with a spherically shaped recess or ball socket 3 engaged by the rounded or ball-shaped lower end of a connecting rod 4. The connecting rod 4 at its opposite or upper end is pivotally connected, at 5, to the lifting member or beam 6 of the crane. The beam 6 is pivotally connected at 7 to a hollow bracket 8 projecting upwardly from the power cylinder 1 and secured to the upper end thereof, such as by welding. Below the piston 2 a pressure chamber 9 is arranged within the cylinder 1. A tube 10 welded to United States Patent 0 M 2,868,175 Patented Jan. 13, 1959 the bottom of this chamber projects upwardly through this bottom. A tube 19 of diameter smaller than that of tube 10 is secured, such as by welding, to the lower end of the tube 10. The tube 10 has inserted in its upper end, and preferably threaded therein, a bushing 11 having a relatively restricted bore 12 therethrough. The bushing 11 is provided with a plurality of fluid ports 13 and is secured, preferably welded, at its lower end to an inner tube 14. The latter is closed at its lower end by an end wall 15 having an orifice 16 formed therethrough and controlled by a main valve 17 adapted to be maintained in its open position by a pressure head acting thereon from the interior of the inner tube. The annular space between the tubes 10 and 14 forms a fluid-flow passageway 18 merging at its lower end into the interior of the tube 19 which is connected to the source of fluid under pressure (not shown).

Depending from the bottom face of the piston 2 is a rod 20 extending through the reduced bore 12 in a man ner to leave an annular space between the rod 20 and the inner wall surface of the bore 12. The rod 20 is provided at its lower end with a plunger or slide-valve 21 having a reduced diameter portion 21 and formed with a central through-bore 22 and a lateral port 23 in the portion 21' providing for fluid communication between the upper and lower sides of the plunger or slide-valve 21. The arrangement described operates in the following manner.

When the piston is to be raised from the position illustrated in Fig. 1 into its top-most position as illustrated in Fig. 2, pressure fluid, such as pressurized oil, is supplied to the interior of the tube 19. The pressure fluid will pass through the passageway 18 and ports 13 into the annular space 12 between the bushing 11 and rod 20. From this annular space 12 a portion of the pressure fluid will enter into the interior of the tube 14 filling up the latter. Thence pressure fluid will enter the pressure chamber 9 below the piston 2 and force the latter upwardly causing the connecting rod 4 to be raised thus elevating the lifting member or crane beam 6. However, as the beam 6 approaches its predetermined limit position the plunger or slide-valve portion 21 enters the reduced bore 12 thus throttling the flow of fluid into the chamber 9 and when the slide valve portion 21 enters the bore 12 no pressure fluid will be able to bypass the slide-valve 21 and enter the pressure chamber 9. This action effectively prevents the piston 2 from being displaced further upwardly and causes the beam 6 to be arrested in the position thus attained. On the other hand, the piston 2 will also be unable to descend as long as the tube 19 is maintained in communication with the source of pressure fluid, since the pressure in the pressure chamber 9 will be maintained by a slight fluid leakage flow past the plunger or slide-valve 21.

The ball-valve 17 has for its purpose to permit drainage of the fluid upon pressure-relief in the tube 19. When this occurs and the parts assume their positions as illustrated in Fig. 2, then the fluid will flow from the pressure chamber 9 through the port 23, the bore 22, the interior of the tube 14 and out through the orifice 16 past the ball-valve 17 being now in its open position. This will cause the piston 2 to begin to descend. As soon as the slide-valve 21 passes out through the lower end of the restricted bore in the bushing 11 fluid-flow will also be permitted through the annular space between the rod 20 and the inner wall of the bushing 11. The lowering speed of the piston will be reduced substantially by the resistance to flow oflered by the orifice 16, and by the possible rate of return flow of the fluid through the tube 19.

What I claim is:

1. A pressure fluid servomotor including a piston displaceable in a power cylinder to a limit position, a slide valve member rigidly connected to said piston for controlling communication between said power cylinder and a slide valve cylinder within which said slide valve member is displaceable and for controlling communication between said slide valve cylinder and a passage adapted to be connected to a source of fluid under pressure, said slide valve cylinder being, along the major portion of its length, of larger diameter than said slide valve member but being of reduced diameter at the portion thereof in the region of the slide valve member corresponding to said limit position to provide slidable sealing engagement with said slide valve member, said slide valve cylinder being closed at its end displaced from said power cylinder, a valve controlled orifice in the lower end of said slide valve cylinder in communication with said passage permitting fiow of fluid from the slide valve cylinder into said passage and preventing flow of fluid into said slide valve cylinder from said passage, said slide valve member having a reduced diameter portion on the side thereof toward said power cylinder and having a bore therethrough placing in communication with each other the portions of the slide valve member disposed at opposite ends of its enlarged portion, said slide valve member acting to restrict communication between said power cylinder and said passage when the reduced diameter portion of the slide valve member is in the reduced diameter portion of the slide valve cylinder and to cut off communication between said power cylinder and said passage when the full diameter portion of the slide valve member is in the reduced diameter portion of the slide valve cylinder.

2. A pressure fluid servomotor including a piston displaceable in a power cylinder to a limit position, a slide valve member rigidly connected to said piston for controlling communication between said power cylinder and a slide valve cylinder within which said slide valve member is displaceable and for controlling communication between said slide valve cylinder and a passage adapted to be connected to a source of fluid under pressure, said slide valve cylinder being, along the major portion of its length, of larger diameter than said slide valve member but being of a diameter, at the portion thereof in the region of the slide valve member corresponding to said limit position, to provide slidable sealing engagement with said slide valve member, said slide valve member acting to cut off communication between said power cylinder and said passage when the slide valve member is in said limit position, said slide valve having a longitudinally extending bore therein providing communication between said power cylinder and said slide valve cylinder, and said slide valve cylinder having a check valve controlled port therein providing for flow of fluid from said slide valve cylinder to said passage and preventing flow of fluid from said passage to said slide valve cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 612,324 Frazier Oct. 11, 1898 635,848 Dutton Oct. 31, 1899 695,675 Ebel Mar. 18, 1902 881,165 Taylor Mar. 10, 1908 1,877,102 Whitesell Sept. 13, 1932 2,266,415 DinZl Dec. 16, 1941 

